Posted by **Jess** on Sunday, September 9, 2007 at 6:44pm.

If a projectile is fired straight up at a speed of 10 m/s, the total time to return to its starting position is about ?

-Hfinal=hinitial+ vinitial*t -4.9t^2

0=0+10t-4.9t^2 when I solved for t I got .49t.Am I suppose to plug .49t back into the equation?

A man leans over the edge of a cliff and throws a rock upward at 4.9m/s. How far below the level from which it was thrown is the rock 2 seconds later?

-For this problem I am suppose to get 9.8m/s and instead got -29.4 m

y = 4.9t - 4.9 t^2. Plug in t = 2s and solve for y.

y(at t=2s) = 9.8 - 4*9.8 = -29.4 m

- Physics -
**bobpursley**, Sunday, September 9, 2007 at 6:59pm
The first is a quadratic. Either factor it, or use the quadratic equation.

On the second, you cannot get 9.8 m/s as a distance, that is a velocity.

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